Photodynamic Therapy (PDT) is a known process in which light of a specific wavelength or waveband is directed to tissues undergoing treatment or investigation that have been rendered photosensitive through the administration of a photo-reactive or photosensitizing agent called a photosensitizer. In this therapy, a photosensitizer having a characteristic light absorption waveband is first administered to the patient, typically either orally or by injection or even by local delivery to the treatment site. Proliferating cells, such as those involved in many eye diseases, may preferentially take up or absorb a number of photosensitizers. Once the drug or photosensitizer has been administered and reaches the target tissue, the tissue is illuminated with light of an appropriate wavelength or waveband corresponding to the absorption wavelength or waveband of the photosensitizer.
The object of the PDT may be diagnostic, where the energy level and wavelengths of light are selected to cause the photosensitizer to fluoresce, thus yielding information about the tissue without damaging the tissue. The object of the PDT may also be therapeutic, where the wavelength of light delivered to the photosensitive tissue under treatment causes the photosensitizer to undergo a photo chemical interaction with oxygen in the tissue under treatment yielding free radical species such as a singlet oxygen, causing local tissue affect.
Typically, the light source used to excite the photosensitizer in PDT is a laser. However, the laser equipment used for PDT is relatively expensive. As an alternative, a non-coherent light source, such as an LED, has been used in PDT as described in U.S. Pat. No. 6,319,273. A typical LED, however, has a limited light output on the order of 350 mW. Moreover, because the LED light is non-coherent, a typical emission angle of a LED used in PDT is 180°. As a result, it is difficult to direct the light output from an LED to the eye without significant light loss.